Increasing regulatory and operational pressure has resulted in the need for hydrocarbons that have low sulfur levels and nitrogen levels. Hydroprocessing, which involves treating a hydrocarbon with hydrogen in the presence of a catalyst, is a conventional method for heteroatom (e.g., sulfur and nitrogen) removal.
Conventional hydroprocessing (i.e., known to those skilled in the art of hydrocarbon upgrading) catalysts generally contain a Group VIB metal with one or more Group VIII metals on a refractory support. Hydrotreating catalysts that are particularly suitable for hydrodesulfurization, as well as hydrodenitrogenation, generally contain molybdenum or tungsten on alumina promoted with a metal such as cobalt, nickel, iron, or a combination thereof. Cobalt promoted molybdenum on alumina catalysts are most widely used when the limiting specifications are hydrodesulfurization, while nickel promoted molybdenum on alumina catalysts are the most widely used for hydrodenitrogenation, partial aromatic saturation, as well as hydrodesulfurization.
One example of the use of a supported bimetallic hydroprocessing catalysts is disclosed in GB 820536, which describes a process for the manufacture of mechanically strong supported catalyst particles comprising combinations of cobalt, nickel, molybdenum, vanadium or tungsten. The patent discloses a nickel tungsten supported catalyst obtained by extruding a wet cake comprising 83 wt. % support material and 17 wt. % of metals compounds followed by calcination at 566° C. Similarly, Russian patent publication RU 2114696 describes a nickel tungsten bimetallic supported catalyst made by mixing basic nickel carbonate, tungstic acid and more than 40 wt. % of a carrier material comprising a special carrier of dry alumina gel and aluminum hydroxide, extruding the mixture, drying and calcining at 350 to 450° C. In addition to supported catalysts, hydroprocessing using bulk bimetallic catalysts (also referred to as “unsupported” catalysts) is also known. However, their hydroprocessing performance is generally inferior to the bulk trimetallic catalysts comprising two instead of only one group VIB metals.
For example, PCT patent application WO 00/41810 discloses bulk bi- and tri-metallic hydroprocessing catalysts. Where the trimetallic bulk catalysts have a significantly higher catalytic activity than a bimetallic bulk catalyst prepared in a similar way in a comparison where the feed contained sulfur but no nitrogen. PCT patent application WO 99/03578 is similar in that a bulk trimetallic catalyst exhibits greater hydroprocessing effectiveness over a bulk bimetallic catalyst. Another example of a bulk trimetallic catalyst out-performing a similarly-prepared bimetallic catalyst is disclosed in PCT patent application WO 00/41811.
Recently, bimetallic bulk catalysts of reduced crystallinity have been described PCT patent application WO 2004/073859. The catalysts, bulk metal oxide catalysts comprising one or more metals of group VIII and one or more metals of group VIb in their oxide or sulphide form and a refractory oxide, are prepared by controlled precipitation of metal compounds, refractory oxide material and alkali compound (preferably ammonia) in a protic liquid, forming an ammonium complex of the metal and refractory oxide materials which is subsequently heated. Similarly, PCT patent application WO 2005/005582 describes the use of a bimetallic Group VIb/GROUP VIII catalyst to prepare lubricating base oil. The bulk catalysts are made by reacting one solid compound comprising the group VIII metal and one solute compound comprising the group VIB metal in the presence of the refractory metal after addition of ammonium solution. The catalyst is amorphous as described by X-ray diffraction (“XRD”) analysis.
There is, therefore, still a need for bulk bimetallic hydroprocessing catalysts that are at least as effective for hydrocarbon hydroprocessing as bulk trimetallic catalysts.